The Difference Between Polishing And Grinding

Grinding and polishing are the same mechanical movement, and their principles are the same. Just in terms of appearance quality, the polished surface brightness is higher than that of the grinding. In fact, polishing can also be said to be a subsequent process of grinding, which can be completed on the same flat polishing machine at the same time. Grinding is divided into coarse grinding and fine grinding. And polishing is divided into rough polishing and fine polishing. In many cases, we only need to process the outer surface in three processes: rough grinding, fine grinding, and fine polishing. With these three processes, the flatness, parallelism, and roughness of the surface of the workpiece are quite high. For some customers whose accuracy requirements are not so high, we can only use the first two processes, or the fine grinding process. However, the specific operation depends on the quality of the appearance of the workpiece itself and the quality required by the customer.

Grinding and polishing can be done on the same flat polishing machine, but the configuration used is different. Grinding requires grinding discs and grinding fluids, and polishing uses polishing fluids and polishing discs, polishing pads, polishing cloths, polishing wheels, etc.

The polishing disc is generally made of felt, rubber, leather, cotton products or pressed cardboard. It is a floppy disk with a certain degree of flexibility. The polishing paste is made of abrasive materials, such as chromium oxide, iron oxide, etc., oleic acid, soft grease, etc. Commonly used abrasives for polishing include electric corundum and iron oxide, which are mainly used for processing steel. Emery and chromium oxide are mainly used for processing aluminum, hard aluminum and copper. Silicon carbide and iron oxide are mainly used for processing iron castings. 

During polishing, the parts are pressed on a high-speed rotating polishing wheel, and under the action of the polishing paste medium, a very thin soft film is produced on the metal surface. It can be eliminated with an abrasive softer than the material of the part without leaving scratches on the surface of the part. Coupled with high-speed friction, high temperature appears on the surface of the part, and the surface material is squeezed to cause plastic flow. This can fill in the original microscopic unevenness of the surface and obtain a very shiny surface, such as a mirror-like surface.

One of the important conditions of the mechanical polishing machine is that there must be a device to transmit the high-frequency axial reciprocating motion with a small stroke to the polishing wheel, so as to continuously intersect the wear marks and eliminate the marks formed on the processing surface. This kind of movement is generally realized by a special mechanism mounted on the main sleeve of a mechanical polishing machine, that is, a vibrator. When using a jig for mechanical polishing, an elastic pad or spring device made of leather, rubber, etc. should be placed on the workpiece.